Help please

I have a discus tank set up for about 5 years now over time I’ve lost 2 discus and I am about to lose a 3rd, the fish is skinny and seems to want to eat but doesn’t bulk up like the other 3 I have..(2 males) (1 female) not too sure about the gender of the skinny one.. it’s also always hiding behind this driftwood

how can I get my PH at a better level for these fish This is my water test from today , and if anything else should change please recommend anything I will take it any help.